This invention relates to a method of identifying the location of a defective roll in a strip processing line where a defective roll causes a visible repeating mark on the material being processed.
In the processing of strip material, e.g. aluminum alloy strip, it is commonplace to pass the strip material between rolls. For instance, during cleaning of aluminum alloy strip, the strip may be passed through cleaning tanks or enclosures where the rolls are hidden from view. In such a situation, a defective roll within the tank may be causing a visible repeating pattern mark on the strip material emerging from the tank. It becomes a very difficult matter to determine which one of the rolls within the tank is in fact the one causing the visible repeating pattern mark on the strip material.
At present, the only way of identifying a defective roll is to either shut down and disassemble the line in order to inspect each roll individually for damage or by lifting rolls from the sheet one by one until the defective roll is identified.
In German Democratic Republic Patent DD 293 068 a defective roll is located by a series of calculations that also involve a factor representing the amount of length extension the strip undergoes as its thickness is being reduced by a rolling process.
There remains a need for a convenient system for detecting defective rolls in a strip processing line, e.g. squeegee rolls found inside the tanks of a strip cleaning operation.
The present invention in its broadest aspect relates to a method of identifying the location of a defective roll in a strip processing line wherein a defective roll causes a visible repeating mark on the material being processed. The strip processing line includes a plurality of laterally spaced pairs of rolls between which the strip material is carried and means for opening and closing the roll pairs. An inspection station is provided downstream of the plurality of rolls to inspect for visible marks or defects on the strip emerging from the rolls and data processing means are provided for selectively opening and closing roll pairs in timed sequence. Actuating means are also provided at the inspection station for actuating the data processing means. In accordance with the method of the invention, when a mark or defect on the strip material passes the inspection station, the data processing means is actuated thereby starting the timed opening of the rolls. When the absence of a mark is detected at the inspection station the timed sequence is stopped. Since the mark appears once with each revolution of a roll, the marks will appear equally spaced along the strip, e.g. at equal time intervals. Thus, the absence of a mark at the expected location (time interval) means that the defective roll was out of contact with the strip at that time. The lapsed time between the timed opening and the detection of the absence of a mark is recorded and compared against a data base indicating the location of a roll relative to the lapsed time thereby identifying the defective roll.
The method is generally used with rolls of equal diameter but may also be used where the rolls have different diameters. Thus, the spacing between the marks on the strip indicates the circumference of the rolls. By having the rolls identified in the data processor according to their circumference (or diameter), when the absence of a mark is recorded, the spacing on the strip is also recorded and relates to the circumference in the memory thereby identifying the defective roll. Also, the roll pairs may be opened individually or in groups. In a situation where two adjacent roll pairs are spaced at a distance along the strip less than the circumference of the rolls, these adjacent roll pairs must open separately from each other in order to separately detect each roll pair by lapsed time. For instance, they may open as parts of two separate groups of rolls that open together.
The operating system relies on time measurements to locate the defective roll. Therefore, if the time interval between the closing of a first roll and the opening of a second roll is set to the time it takes a point on the sheet surface to move a distance of at least one full roll circumference, then the system is able to detect the single roll that is causing the defect.
In a preferred embodiment, when a visible repeating mark or defect is noted on the strip material, an operator goes to an inspection station at the downstream end of the processing tank or enclosure. The inspection station includes a marker adjacent the strip material and a data processing unit which includes an activating push button and a signal light. In order to conduct a test, the operator first slows down the line to an inspection speed, e.g. about 10 mpm. When a mark or defect on-the strip material is observed to pass the marker, the push button is immediately activated. This sets in motion a timed sequence measured from the first roll pair at the entry to the processing tank or enclosure. The data processor calculates the time required for a point on the strip to move from the entry point to the marker of the inspection station and provides a signal when that time has lapsed. If at that point in time a mark or defect does not pass the indicator, then the operator immediately pushes the button to end the test. The time is recorded and compared against a data base and a screen at the inspection station indicates which roll pair has caused the mark or defect.
It is also possible to fully automate the procedure to detect the defective roll. Instead of an operator at the inspection station, a scanning system, e.g. a computerized camera system, may be used which is adapted to detect a mark or defect on the strip material. Thus, to conduct a search for a defective roll, the system is activated and when the scanner detects a mark or defect passing the inspection station the timed sequence is started as described above. Then, within a narrow time range within which the mark or defect should again appear, the scanner is again activated. If no mark or defect is detected within that narrow time range, the time is recorded and compared against a data base in the processor and the defective roll is identified.